SF Generator Circuit- Breaker System For Short-circuit Currents Up To .
Technologies for the Utility IndustrySF6 generator circuitbreaker system forshort-circuit currentsup to 200 kALukas Zehnder, Jochen Kiefer, Dieter Braun, Thomas SchoenemannGenerator circuit-breakers arethe ‘big boys’ of the breakerworld; they have to be.A fault of up to 200 kAsomewhere in the field is badenough, but close to agenerator it can lead to anevent of literally seismicproportions – the fault currentcan be of such a magnitudethat the induced magneticforces cause solid steel shaftsto bend and crash.ABB HEC 7/8 SF6breakers are designed for thisdemanding task. They canhandle anything even the world’s biggest power stations can throw at them.But just how do you break such a huge current so close to the generator? And how canthe breaker effectively deal with the arc that is produced?The past twenty years have seenrapid change in the generatorcircuit-breaker field, from the firstbreaker to use SF6 gas as an arc-extin-34guishing medium in the 1980s to thenewest breakers, described in thisarticle, rated at 24,000 A (naturallycooled) and 38,000 A (with forced aircooling) and able to handle short-circuitbreaking currents of up to 200 kA.Thanks to these developments,modern special-purpose generatorABB Review 3/2002
circuit-breakers using SF6 gas as arcextinguishing medium are now availablefor generating units with ratings up to1500 MW.switches (for gas turbine and hydropower plants) and braking switches(for hydropower plants) can also beintegrated 1 .Master of all tradesHigh availability and low costA modern breaker has to perform manytasks:n Synchronize the generator with themain systemn Separate the generator from the mainsystemn Interrupt load currents (up to the fullload current of the generator)n Interrupt system-fed and generatorfed short-circuit currentsn Interrupt currents under out-of-phaseconditions (up to 180 )Not surprisingly, all power plantoperators give a top priority to havingthe highest possible plant availability atthe lowest possible cost. Modern SF6generator circuit-breaker systems helpachieve this:n The differential protection zones ofthe generator, the main transformer andthe unit transformer can be arranged toachieve maximum selectivity.n Generator-fed short-circuit currentsare interrupted within a maximum offour cycles, as opposed to severalseconds using rapid de-excitationequipment.A generator circuit-breaker’s performance must be far better than that of anMV breaker; the positioning of thegenerator circuit-breaker systembetween the generator and the maintransformer, where its performancedirectly influences the plant output,places very high demands on itsreliability.Also, modern generator switchgearconsists of much more than just aninterrupter unit: All the associatedequipment can nowadays be integratedin the generator circuit-breaker enclosure, for example a series disconnector,grounding switches, a short-circuitingswitch, current transformers, single-poleinsulated voltage transformers, protective capacitors and surge arresters.Depending on the type of power plant,additional items such as startingABB Review 3/20021The overall availability of the powerplant auxiliary equipment is increased.n Synchronizing at the generatorvoltage level with the help of agenerator circuit-breaker is considerablymore reliable than synchronizing with ahigh-voltage circuit-breaker [1].n Rapid changeover to the auxiliarysupplies during unit start-up and shutdown, with the associated high inrushcurrents and resulting stresses, is eliminated, thus avoiding possible damageto the drive motors of pumps, fans,etc.n Use of generator circuit-breakersallows plant auxiliary supplies to bedrawn directly from the HV transmissionsystem at all times, ie also during thecritical start-up and shut-down phases.This is considerably more reliable thanother sources.nGeneral layout of ABB's generator switchgear1Circuit-breaker8Starting switch (‘back-to-back’)2Disconnector9–12Voltage transformers3, 4Earthing switches13, 14Current transformers5/6Starting switch15Surge arrester(SFC or ‘back-to-back’)16, 17Surge capacitorsShort-circuiting 2191818GT1316 315/62417 1514835
Technologies for the Utility Industry152chamber, with the contact closed267831094121311Rapid interruption of generator-fedshort-circuit currents reduces consequential fault damage and shortensrepair times.n3The higher plant availability andincreased profit for the operator make amodern generator circuit-breaker anexcellent investment, with a generallyvery short payback time.Contact movements and current versus time curve1Movement of arcing contactt1Drive tripped2Movement of main contactt2Main contact system separates3Current curvet3Arcing contact system separatest4Arc extinguished at zero current4Voltage across breaker5Pressure build-up phase6Arc extinguished at zero current3412t136t2t3Cross-section through the arcing1Housing2Main contact system3Arcing contact system4Arcing contact system (pin)5Insulator6Piston(s)7Gearing8Drive9Heating gap10Heating volume(segmented part)11Gas-return channels12Overpressure valve13Non-return valvesThe circuit-breakerBesides conducting and interruptingoperating currents, the circuit-breaker –a chamber filled with SF6 gas underpressure – has the job of interrupting ACfault currents, eg short-circuit currentsfive or ten times the value of the ratedcurrent, within about 50 milliseconds.The pressure chamber in which thecurrent interruption takes place consistsbasically of two metal housings, whichalso act as electrical conductors, and theinsulator.Both contact systems – the maincontact system and the arcing contactsystem – as well as the associatedconcentrically mounted blast pistonsare coupled to internal gearing which isconnected to a high-speed drive situatedoutside this chamber.The gearing is designed such that,during breaking, the main contactsystem parts a few milliseconds beforeABB Review 3/2002
4Cross-section through the arcing chamber showing the hot gas flow paths(arrows) during the pressure build-up phase (left) and the current’s passage throughzero (right)the arcing contact system, ensuring thatthe full current is broken by the latter.The arc created when the arcing contactsystem separates is extinguished theinstant the alternating current nextpasses through zero 3 .During making, the procedure isreversed; the rising voltage leads to anarc in the closing arcing contact systemjust before contact is made; the maincontact system then closes to carry thefull current.Arc extinction principleLike its smaller brothers (see Table onpage 38) the HEC 7/8 utilizes the selfblast principle to extinguish the arc, iethe energy required by the gas streamfor arc extinction is derived from thearc itself.The energy released by the arc’screation leads to a very rapid and largelocal pressure and temperature rise. Theconvective and radiative heat from thearc causes a sudden rise in pressure inthe ‘heating volume’ between the arcingcontact system and the piston 4 . It isfrom here that hot gas is blasted toextinguish the arc the next time thealternating current passes through zero.A further contribution to the pressurerise is provided by the magnetic fieldpinch effect in the arc’s interior, beingmanifested as a force acting in thedirection of the center of the arc path.This current-generated magnetic force,in turn, causes a strong axial flow out ofthe arc, basically a plasmajet whichshoots outwards and is partly divertedinto the heating volume 5 .ABB Review 3/2002When very high currents are flowingduring breaking, the pressure rise canbe quite dramatic. Mechanical damage isavoided by relieving the pressure via aspecial overpressure valve. This valvewas designed in conjunction with ABBCorporate Research as part of anexperimental program to measure thepressure rise in the heating volume, inthe flowback passages and in theplasmajet itself.The relatively low arc energy at lowcurrents is unable to create enoughpressure for a significant self-blasteffect. This is where the concentricallymounted blast pistons come in; by5Geometry(top), photo(center) and flowsimulation(bottom) of aplasma jet withshock zones.The plasma jetoriginates in thearcing zone (lefthand edge) andstrikes theoverpressurevalve (right-handedge).37
Technologies for the Utility Industrysupporting the pressure build-up in theheating volume it helps to ensuresuccessful blasting, and extinction, ofthe arc.12Passage through zeroShortly before the alternating currentpasses through zero, the arc crosssection, the pressure in the arc zone andlocal heating effects all significantlydecrease.If the contact separates just beforethe current passes through zero then thepressure build-up in the heating volumemay be too weak to extinguish the arc.In this case, the breaker waits a halfcycle until the next passage throughzero, by which time sufficient pressurehas built up.Touch and goThe arcing contact system is, quiteliterally, where the action is. With peakcurrents of up to 600 kA to handle, the346A finger of the segmented arcingcontact system1Flange2Contact finger3Connecting part4Arc-resistant tipdesign of this system has to fulfill aquite extraordinary set of criteria:n A reserve of material sufficient toallow for ablation over the lifetime ofthe apparatus, bearing in mind theextreme plasma conditions that have tobe endured.n Lowest possible metal ablation rateto minimize contamination andconsequent degradation of theinsulating gas.n Mechanical stability in the face ofpowerful switching and electrodynamicforces.n Optimal contact force over the entirecurrent range by careful balancing ofantiparallel (repulsive) and parallel(attractive) current paths.n Guarantee of low electrical resistanceand high thermal conductivity.The contact itself consists of a centralrod grasped by segmented ‘fingers’. 6shows the construction of an individualfinger. The material used for the base (1,2) is a springy copper alloy (CuCrZr),while for the arc-resistant tip (4) awolfram-copper composite (5) is used.Technical data of ABB’s SF6 generator circuit-breakersTypeHGC 3HEC 3/4HEC 5/6HEC 7/8Rated maximum21 kV25 kV25 kV30/25 kV50/60 Hz50/60 Hz50/60 Hz50/60 HzUp to 7700 AUp to 13,000 AUp to 13,000 AUp to 24,000 ANot applicableUp to 24,000 AUp to 24,000 AUp to 38,000 A63 kA100 kA120 kA160/200 kAIEEE C37.013IEEE C37.013IEEE C37.013IEEE C37.013voltageRated frequencyRated continuous current:n with naturalcoolingn with forced-aircoolingRated short-circuitbreaking currentStandard38ABB Review 3/2002
The bond between the base and the tipis also made of copper (3).Thermal considerationsThe thermal design of the breakersystem is based on the assumption thata constant current flows at the ratedvalues in a 40 C environment. Themaximum temperature allowed of anyhot spots on the silver-plated contacts is105 C. Outer parts that can be touchedmay not exceed 70 C (in some cases80 C).The encapsulated design has theadvantage that it includes both the innerconductor current and the outer returncurrent flow path. As these are 180 outof phase, the external field strength, andthus external heat generation, isconsiderably reduced.Two-dimensional finite elementanalysis of current distribution in certaincomponents was used to reveal areasof high current and high loss as well asthe degree to which the skin effectimpedes current flow at differentfrequencies.Physical verification was used in aniterative process to improve model accuracy, and led to an optimal conductorcross-section and an ideal thermallayout of the system.Specially designed fins around thehousing of the interrupter 7 increaseits surface area to maximize heat dissipation. Forced-air cooling, by improvingthe convective heat transfer, allows the24-kA nominal current with naturalcooling to be raised to 38 kA.ABB Review 3/20027Interrupter housingInsulation materialA cooperative venture between ABBCorporate Research and a Swiss company, Vantico, succeeded in developingan epoxy resin capable of withstanding105 C for 30 years [2]. With a diameterof 1 meter, the physical dimensions ofthis insulator are noteworthy 7 .TestingProducing a breaker to handle hundredsof kiloamperes is one thing, but howdo you test it? Fortunately, ABB has itsown laboratories in Switzerland whereshort-circuit test currents of up to 450kA can be generated. As the HEC 7/8 isspecified up to a peak value of 600 kA,further tests were carried out in theKEMA high-power test laboratory 8 inArnhem, The Netherlands. The facilitieshere offer the highest test powersanywhere in the world.The scale of the tests at KEMA canbe appreciated by the fact that theyinvolved an eight-strong ABB teamgoing to Arnhem for over three months,taking with them no less than five lorryloads of equipment.These tests were for 160 kA and30 kV and were completed in May 2000.Interest in higher current ratings led toan intensive analysis and simulation,culminating in autumn 2001 with afurther test series at KEMA, this time at190 kA for 27.5 kV and 200 kA for25 kV. These ratings just about matchthose of the DR air-pressure generatorbreaker that has until now dominated39
Technologies for the Utility Industrystandards possible. ABB subsequentlyimplemented these measures in itsbreaker production facilities.World’s finestThe design of breakers for the world’sbiggest generators needs to be worldclass. Successful cooperation betweenmany different research and development units, including external partners,fostered the key breakthoughs andinnovative climate essential to ensurethis.The HEC 7/8 meets, and exceeds, theperformance expected by this high-endmarket, and in so doing has proveditself to be not just the world’s biggestSF6 breaker and the most rigorouslytested, but also the best. At the sametime, it sets new economic standards –standards that will guarantee itscompetitiveness in the marketplace.8 Type testing in the KEMA high-power test labthis application area, and which is nolonger produced.Based on these tests, the HEC canquite justifiably claim to be not only theworld’s largest SF6 breaker, but also thebest and most thoroughly tested.ReliabilityReliability obviously rates a top priorityat the high end of the generator market.To take account of this, a failureanalysis methodology refined in the1960s for aerospace projects wasemployed to define measures thatwould ensure the highest reliabilityAuthorsDr. Lukas ZehnderDr. Jochen KieferDieter BraunDr. Thomas SchoenemannABB Switzerland Ltd.High Current Systems PTHGCH-8050 rences[1] I. M. Canay, D. Braun. G. S. Köppl: Delayed current zeros due to out-of-phase synchronizing. IEEE Transactions on Energy Conversion, 13 (1998)2, 124–132.[2] K. Guzek, M. Claessens, S. Förster: Starker Schalter. ‘akzent’, ABB Switzerland journal, December 2000.40ABB Review 3/2002
SF6 generator circuit-breaker system for short-circuit currents up to 200 kA Lukas Zehnder, Jochen Kiefer, Dieter Braun, Thomas Schoenemann Generator circuit-breakers are the 'big boys' of the breaker world; they have to be. A fault of up to 200 kA somewhere in the field is bad enough, but close to a generator it can lead to an event of .
Circuit-breaker with RHE RHD Circuit-breaker with HTC Circuit-breaker with LTC Circuit-breaker with FLD A IP 40 IP 20 IP 40 IP 40 IP 40 IP 40 B IP 20 IP 20 IP 20 IP 40 IP 30 IP 20 (1) During installation of the electrical accessories Weights A1 [Kg] A2 [Kg] A3 [Kg] Circuit-breaker 1 pole 0.245 0.37 - Circuit-breaker 2 poles 0.47 0.73 - Circuit .
electronic trip circuit breaker A circuit breaker which uses current sensors and electronic circuitry to sense, measure and respond to current levels. fixed-mounted circuit breaker A circuit breaker so mounted that it cannot be removed without removing primary and sometimes secondary connections and/or mounting supports.
With the recent successful certification of a 160 kA-generator circuit-breaker modern SF 6 generator circuit-breakers are now available for generating units up to 1400 MW. Another new development has been the integration of all the associated items of switchgear within the generator circuit-breaker enclosure as an option to their separate .
Student Manual Circuit Breaker Cubicle USNRC 4-1 Rev 0 4.0 CIRCUIT BREAKER CUBICLE Learning Objectives The circuit breaker cubicle is the component of the switchgear that holds the circuit breaker,
System pro M compact Miniature Circuit Breaker SU200 M for branch circuit protection acc. to UL 489 Data Sheet The miniature circuit breaker SU200 M is ABB's solution for UL 489 branch circuit protection up to 480 Y/277 V AC and 96 V DC. This circuit breaker is an all-round device for AC and DC applications for universal use in North
Content Products Trends in High Voltage Circuit Breaker Technology 4 Dead Tank Based Compact Switchgear 8 Bypass Circuit-Breaker for 800 kV DC 13 1200 kV AC substations:Full-scale products and integrated solutions 19 Circuit-Breaker Platform for 550 kV 27 Siemens High-Voltage Circuit-Breakers for Use at Low Temperatures 34 3AP4/5 High-Voltage Circuit-Breaker for 800 kV 41
5.1 Circuit breaker offered shall be sulphur hexaflouride (SF6) type only. 5.2 Any part of the breaker, especially the removable ones, shall be freely interchangeable without the necessity of any modification at site. 5.3 Circuit breaker shall comprise of three identical single pole units. If the circuit breaker
Introduction to Academic Writing This study pack is designed to take about 50 minutes. It will give you an introduction to academic writing, sharing the most important principles that will guide you through writing during your degree at UCL. It was put together by the Writing Lab, which is the section of the Academic Communication Centre(ACC) that serves students from Bartlett; Psychology .
